The present invention generally relates to abrasive bodies and more particularly to diamond and cubic boron nitride abrasive compacts or inserts.
Abrasive compacts are well known in the art and consist essentially of a mass of abrasive particles present in an amount of at least 70 percent by volume bonded to a hard substrate. The abrasive particles of compacts are invariably superabrasives, such as diamond and cubic boron nitride, and the hard substrate is usually a carbide such as tungsten carbide, titanium carbide, tantalum carbide or a mixture thereof. Abrasive compacts, particularly diamond and cubic boron nitride compacts, may be self-bonded, i.e., the individual particles of the compact are fused and bonded together without the aid of a metal or like bonding matrix. Alternatively, compacts may be produced where there is a suitable bonding or cementing matrix present.
Diamond and cubic boron nitride compacts can be used for the machining of metals. In use, the compacts are fastened to a suitable tool support such as a shank to form a tool. The compacts may be fastened to a backing such as a cemented carbide backing and then the backing fastened to the support to form the tool.
U.S. Pat. No. Re. 32,380, assigned to the same assignee as the present invention, describes a diamond compact comprising (a) a diamond crystalline mass wherein the concentration of diamond is in excess of 70 percent by volume and in which the diamond crystals are disposed in random fashion and substantially all of the diamond crystals are directly bonded to adjacent diamond crystals and (b) a support material which is a cemented carbide mass considerably larger in volume than the volume of the diamond crystalline mass, the diamond crystalline mass and the cemented carbide mass being joined at an interface consisting of cemented carbide, or its elements and diamond crystals.
U.S. Pat. No. 3,767,371, assigned to the same assignee as the present invention, describes an analagous cubic boron nitride compact comprising (a) a unified mass of greater than 70 volume percent cubic boron nitride crystals bonded to (b) a supporting mass of metal bonded carbide selected from the group consisting of tungsten carbide, titanium carbide, tantalum carbide and mixtures thereof; the bonding material being selected from cobalt, nickel, iron and mixtures thereof and the interface between the mass of cubic boron nitride crystals and metal bonded carbide support being free of voids. U.S. Pat. No. 3,743,489, also assigned to the same assignee as the present invention, teaches that further including aluminum with the bonding medium results in superior bonding of the cubic boron nitride crystals to each other as well as between the cubic boron nitride mass and the carbide substrate.
U.S. Pat. No. 4,224,380, assigned to the same assignee as the present invention, describes thermally stable diamond and cubic boron nitride compacts wherein the bonding material, for example cobalt or cobalt alloys, is removed so as to provide compacts having substantially 100% abrasive particles and which therefore can withstand exposure to temperatures of 1200.degree. C. to 1300.degree. C. without substantial thermal degradation. The compacts can be made only of self-bonded abrasive particles or they can be made of self-bonded particles bonded to a substrate such as cemented carbide.
U.S. Pat. No. 4,229,186 discloses a laminated abrasive body which is in effect a thick compact comprising a plurality of diamond or cubic boron nitride compacts laminated together by means of a metal or metal alloy braze. Such laminated abrasive bodies are said to be useful as a high pressure piston in an apparatus for obtaining ultra-high pressures on the order of megabars.
All of the foregoing patents are incorporated by reference into the present disclosure.
Although supported and unsupported superabrasive compacts have been found to be of great value in the metal-machining field, they all suffer from the disadvantage that once the superabrasive mass is worn or damaged, the compact must be disposed of and a new compact inserted in its place. Furthermore, unsupported superabrasive compacts have lower toughness and tend to form cracks under repeated bend loading conditions encountered in high speed machining operations. The cracks so initiated in the body of the insert propagate easily due to lower toughness of the insert and cause it to break into many pieces. It has now been discovered that these disadvantages can be minimized by employing compacts having superabrasive masses bonded to each of the upper and lower surfaces of a support mass. Thus, when one superabrasive mass is damaged, for example, by cracking or chipping, the compact is simply turned over and the other superabrasive mass used to combine the machining operation. Moreover, any such crack cannot reach the other side of the insert due to the presence of the tough support mass between the superabrasive layers.